The present invention relates to apparatus for feeding loose materials from a storage container into pneumatic conveyors and in particular to a dossimeter for feeding loose granulate materials into pneumatic conveyor conduits.
Apparatus enabling the feeding of loose material continually from a storage chamber such as a silo, subjected to any desired pressure, into a pneumatic conveyor conduit having therein a higher or lower prevailing pressure are generally known under the appellation of "bucket wheel locks". Such apparatus comprises a housing in which a bucket wheel having a hub fixed on a horizontal shaft is rotably journalled in the housing. The wheel has a plurality of radially extending wings or blades which define wedge shaped or trapezoidal chambers or buckets. Loose granular material is fed to the housing through an upper inlet opening where it falls onto each of the buckets successively and from which, after a rotation of approximately 180 degrees it is transferred via an oulet opening into the pneumatic conveyor conduit. If necessary, the transfer of the loose material into the conveyor conduit is assisted by the use of compressed air.
The amount of loose material dosed in this manner increases at first, with the rising speed of the bucket wheel, but decreases again with an additional increase of speed thereof. This is caused by the centrifical forces acting upon the bucket wheel and the loose material. The maximum amount of loose material dosed in any given time period is achieved at a bucket wheel speed of approximately 20-40 rpm.
An additional disadvantage occurs if a higher pressure prevails in the receiving pneumatic conveyor conduit than at the inlet opening of the bucket wheel lock. Since the design must insure rotation of the bucket wheel in the housing, the space between the bucket wheel itself and the housing, causes the air flowing from the high pressure conveyor conduit to run in the opposite direction to that of the falling loose material, preventing the complete filling of the bucket wheel chambers. This is a particularly troublesome fact when fine grained loose material is being transferred. Finally, problems are also encountered with viscous, sticky, and randomly sized "bridge-building" particulate loose materially. Because of the relatively narrow inlet sections required for the construction of such apparatus, such materials act to interrupt the continuous filling of the bucket wheel chambers.
It was also known to mount the bucket wheel so as to be rotatable about a vertical axis. The loose material is fed into the housing via an eccentric opening, which corresponds approximately to the cross-section of the buckets, and after being further transported approximately 180 degrees, is blown out of the bucket wheel chamber through an axial opening into the conveyor conduit. A burst of clear air is used to assist the discharge, the mouth of the clearing air duct being located exactly axially to the outlet. A disadvantage of this construction resides in the fact that the narrow cross-section of the inlet prevents a continuous flow of the loose material to be dosed and even makes such a continuous flow impossible when cohesive and sticky loose materials are transported.
It is an object of the present invention to provide apparatus of the type described which permits a high dosage rate even for viscous, sticky, loose materials.
These objects together with other objects and advantages will be apparent from the following disclosure.